1. Field of the Invention
The present invention relates generally to a reproducing apparatus for reproducing a color video signal which is recorded in such a manner that a pair of component chrominance signals are time-base-compressed, time-division-multiplexed and then recorded on a track different from a track on which, for example, a luminance signal is recorded at the same time with the luminance signal. More particularly, this invention relates to a video signal reproducing apparatus in which a dropout compensation circuit system is simplified in circuit arrangement.
2. Description of the Prior Art
As a recording and reproducing apparatus such as a video with a camera integrally therewith and other recording and reproducing apparatus (VTR), there is proposed such a recording and reproducing system (see a published document of Japanese patent application unexamined No. 56-134891) in which a color video signal is separated into a luminance signal and a pair of component chrominance signals and they are then respectively recorded on different tracks. According to this recording and reproducing system, a pair of component chrominance signals, for example, a pair of color difference signals R-Y and B"Y are time-base-compressed to the half and time division multiplexed as shown in FIG. 1B and the time base-compressed chrominance signals (hereinafter referred to as compressed color difference signals) are recorded on the track adjacent to a recording track of a luminance signal Y.
FIG. 2 is a block diagram illustrating a practical example of a recording and reproducing apparatus which can realize such recording and reproducing system.
In FIG. 2, reference numeral 10R generally designates a recording system. This recording system 10R will be described first. Referring to FIG. 2, a luminance signal Y containing a horizontal synchronizing signal P.sub.H and applied to a terminal 1 is added with a first synchronizing signal (pulse) P.sub.Y used for matching the time between channels by an adder 2. As shown in FIG. 1A, the synchronizing pulse P.sub.Y is inserted into and added to, for example, the latter half portion of the horizontal synchronizing pulse P.sub.H with the polarity opposite to that of the synchronizing pulse P.sub.H.
The reason why the synchronizing pulse P.sub.Y with the positive polarity is inserted into the latter half of the horizontal synchronizing pulse P.sub.H is to facilitate the synchronizing separation of the pulse P.sub.Y and to prevent a spurious to the low frequency band component of the luminance signal Y by the pulse P.sub.Y whereby to avoid the occurrence of moire.
Reference W.sub.H denotes the pulse width of the pulse P.sub.H and, in this example the pulse width of the synchronizing pulse P.sub.Y is selected as 1/2W.sub.H.
The luminance signal S.sub.Y having the synchronizing pulse P.sub.Y inserted is frequency-modulated by an angular modulator, for example, an FM modulator 3 to be a frequency-modulated luminance signal S.sub.Y and then recorded on a magnetic medium, for example, a tape 4, in this example, by a head Ha.
On the other hand, the red and blue color difference
signals R-Y and B-Y are time-base-compressed to the half by a time-base-compressor 5 and then time division multiplexed. The compressed signals R-Y and B-Y are added with a second synchronizing signal (pulse) Pc by an adder 6, forming a compressed color difference signal Sc shown in FIG. 1B.
In order for the second synchronizing pulse Pc to be used for matching the time between the channels, it is inserted into the compressed color difference signals R-Y and B-Y at the time position same as the time position at which the first synchronizing pulse P.sub.Y is inserted. In this example, the second synchronizing pulse Pc is inserted under being the state of the negative polarity.
The compressed color difference signal Sc is frequency-modulated by an FM modulator 7 to be a frequency-modulated color difference signal Sc' and then recorded on the tape 4 by a head Hb. In this case, a recording track for the compressed color difference signals is formed so as to adjoin the recording track for the luminance signal S.sub.Y.
Reference numeral 10P designates a reproducing system, in which the luminance signal S.sub.Y ' reproduced by the head Ha is supplied through an amplifier 11 to a demodulator 12 and thereby frequency-demodulated.
In like manner, the compressed color difference signal Sc' (shown in FIG. 3A) reproduced by the head Hb is supplied through an amplifier 13 to a demodulator 14 and thereby frequency-demodulated to be the signal Sc (FIG. 3B). The demodulated signal Sc is time-base-expanded twice by a time base expander 15 and a pair of color difference signals R-Y and B-Y are produced at the same timing. At that time, since the time base expander 15 is supplied with a read clock the time base of which is constant, the time base expander 15 generates the color difference signals R-Y and B-Y the reproduced jitter components of which are removed (FIGS. 3D and 3E).
The pair of color difference signals R-Y and B-Y are fed to a signal compensator circuit 20 which forms a dropout compensator circuit 16. The signal compensator circuit 20 is provided for the respective transmission systems of the pair of color difference signals R-Y and B-Y. In this example, the circuit 20 is formed of 1H (H is the horizontal period) delay circuits 21 ans 23 and switching circuits 22 and 24. The switching circuit 22 is supplied with the red color difference signal R-Y derived from the time base expander 15 and the output signal from the delay circuit 21, while the output signal from the switching circuit 22 is supplied to the delay circuit 21.
Similarly, the other switching circuit 24 is supplied with the blue color difference signal B-Y derived from the time base expander 15 and the output signal from the delay circuit 23, while the output signal from the switching circuit 24 is supplied to the delay circuit 23.
When a dropout occurs, the pair of switching circuits 22 and 24 are supplied with a switching pulse (dropout compensating pulse) which is used to replace the color difference signal with the dropout by the color difference signal before the same by 1H. To this end, the frequency modulated and compressed color difference signal Sc' passed through the amplifier 13 is further supplied to a dropout detector circuit 17 which generates a dropout pulse DO shown in FIG. 3C, when it contains a dropout. The dropout pulse DO is supplied to a time base expander 18 in which the time base of the dropout pulse DO is expanded twice (FIG. 3F).
Since the time base expander 18 generates a dropout pulse corresponding to a dropout interval, if a dropout occurs in, for example, an interval a shown in FIG. 3A, only the blue color difference signal B-Y in the compressed color difference signal Sc' is dropped out, so that the time base expander 18 generates only a dropout compensating pulse DO.sub.B for the color difference signal B-Y.
Dropout compensating pulses DO.sub.R and DO.sub.B from the time base expander 18 are supplied through an OR circuit 19 to the pair of switching circuits 22 and 24 commonly, whereby the dropout is compensated for both the color difference signals, simultaneously (FIGS. 3G and 3H).
The reason why the red color difference signal R-Y is also simultaneously compensated for even when the dropout occurs in only the blue color difference signal B-Y will be described. That is, if the red color difference signal R-Y is not compensated for by the color difference signal on the same horizontal line but only the blue color difference signal B-Y is compensated for by the blue color difference signal B-Y 1H preceding, color display is carried out by color difference signals of different horizontal lines and hence there is then a fear that depending on the picture images, a hue is disturbed and accordingly the quality of picture will be deteriorated.
A reproducing apparatus in which a pair of color difference signals are both compensated for simultaneously has already been proposed by the assignee of the present application (see, for example, the specification of Japanese patent application No. 58-62750 and so on).
The pair of color difference signals R-Y and B-Y whose dropout is compensated for are supplied to an encoder 26 and thereby converted to a chrominance signal C. This chrominance signal C and the above mentioned luminance signal Y are supplied to a composer or synthesizer 27 so that a video signal S.sub.V of the signal format according to the standard system is developed at a terminal 28 led out therefrom.
A pair of color difference signals R-Y and B-Y shown in FIGS. 3I and 3J are the output signals derived from the delay circuits 21 and 23, respectively.
By the way, in the recording and reproducing apparatus constructed as mentioned above, when the dropout is compensated for by the manner described above, the dropout pulse DO is once time-base-expanded and then the dropout is compensated for by using such dropout pulse DO. This requires the reproducing system 10P to have the time base expander 18 for the dropout pulse in addition to the time base expander 15 for the color difference signals. When a charge transfer element such as a CCD (charge coupled device) is used as the time base expanders 15 and 18, at least two CCDs must be prepared for one pair of color difference signals R-Y and B-Y, thus to increase the circuit scale.
Further, the timing at which the dropout should be compensated for must be controlled accurately, otherwise the dropout compensation can not be carried out at the correct position. This makes a read clock control system for the time base expander 18 complicated in construction.